In next generation multimedia mobile communication systems, which have been actively studied in recent years, there is a demand for a system capable of processing and transmitting a variety of information (e.g., video and wireless data) in addition to the early voice-oriented services. In order to maximize efficiency of a limited radio resource in the mobile communication systems, methods for more effectively transmitting data in time, spatial, and frequency domains have been provided.
Orthogonal frequency division multiplexing (OFDM) uses a plurality of orthogonal subcarriers. Further, the OFDM uses an orthogonality between inverse fast Fourier transform (IFFT) and fast Fourier transform (FFT). A transmitter transmits data by performing IFFT. A receiver restores original data by performing FFT on a received signal. The transmitter uses IFFT to combine the plurality of subcarriers, and the receiver uses FFT to split the plurality of subcarriers. According to the OFDM, complexity of the receiver can be reduced in a frequency selective fading environment of a broadband channel, and spectral efficiency can be increased when selective scheduling is performed in a frequency domain by using a channel characteristic which is different from one subcarrier to another. Orthogonal frequency division multiple access (OFDMA) is an OFDM-based multiple access scheme. According to the OFDMA, efficiency of radio resources can be increased by allocating different subcarriers to multiple users.
To maximize efficiency in the spatial domain, the OFDM/OFDMA-based system uses a multi-antenna technique which is used as a suitable technique for high-speed multimedia data transmission by generating a plurality of time and frequency domains in the spatial domain. The OFDM/OFDMA-based system also uses a channel coding scheme for effective use of resources in the time domain, a scheduling scheme which uses a channel selective property of a plurality of users, a hybrid automatic repeat request (HARQ) scheme suitable for packet data transmission, etc.
In order to implement various transmission or reception methods to achieve high-speed packet transmission, transmission of a control signal on the time, spatial, and frequency domains is an essential and indispensable factor. A channel for transmitting the control signal is referred to as a control channel. There are on-going active discussions on various methods in which the transmitter performs effective retransmission according to feedback information received from the receiver in order to maximize efficiency of limited radio resources.
Since system reliability is dependent on reliability of the control signal, the control signal needs to be detected from the control channel with higher reliability. Therefore, there is a need for a control channel structure robust to a variable channel environment while increasing user equipment capability and transmission capability.